Historically, the primary task of an air filter has been to reduce the amount of particulate matter that might normally enter into an internal combustion engine. Even small abrasive particles could cause significant damage to an internal combustion engine resulting in expensive repairs.
In practice, unfiltered air is directed through the filter, which is often a material chosen for its ability to capture particles of particular range of sizes. The air then exits the filter and is directed into the engine.
There immerged numerous types of filters. Some were dry filters while others used oil to absorb particles. The geometries of the filters also varied to increase the surface areas of the filter without impacting the size of the filter.
However, with all these developments usually the filters were placed in close proximity to the internal combustion engine. This resulted in the air entering the filter being directed into the engine compartment of the vehicle. As the engine gave off heat as a by-product, the intake air became hotter than the outside ambient air.
It was discovered that if the intake air were cooler than the temperature in the engine compartment, then engine efficiency increased. This phenomenon has been credited by many to the application of the ideal gas equation.
Per the equation, temperature and volume of a gas are directly related. As the temperature drops the volume of the air decreases resulting in an increase in the density of the air.
In relation to an internal combustion engine, the increased density provides more Oxygen to combine with the hydrocarbon fuel and therefore a more efficient burn.
There arose a number of approaches to reduce the temperature of the intake air. This proved to be a challenge since the filter systems were in such close relation to the engine.
One approach was to separate the air filter assembly from the rest of the engine compartment. This is usually done with a barrier such as a wall or box type enclosure around the air filter. FIG. 1 shows one such enclosure. The filter apparatus 10 has a housing 15 and a cover 29 that encloses a filter. The air is drawn into the housing through the input opening 20. Once the air is filtered, the air is directed through the housing to an air inlet tube 25 then to the engine.
This configuration exemplifies a case where there is a channel 23 incorporated as part of the cover that focuses the air flow into the air inlet tube 25. Other units interface with the air inlet tube by having the tube pass through a wall or barrier of the housing and extending into the housing before coming into contact with the air filter. These cases are generally less expensive, but also allow for heat transference through the interface between the air inlet tube and the housing.
This approach requires screws 27 and other parts such as a separated wall to create the enclosure. Furthermore, it is evident that the filter must be fitted into the enclosure before being sealed with the wall and screws. This requires time and effort and reduces the efficiency to install and maintain the filter system.
FIG. 2 identifies another assembly with another type of housing. This filter assembly 30 has the filter 35 separated from the engine compartment by a housing 40 that is not completely enclosed as in FIG. 1. While this unit does not require as much work to install and maintain as the system in FIG. 1, the unit in FIG. 2 is not as efficient in isolating the filter from the heat of the engine. This is due to the partial enclosure. The hood of the vehicle covers the top of the filter assembly. That contact is not as efficient as a full enclosure.
The configuration also requires the air inlet tube 45 to extend into the housing and connect with the filter 35. This allows for heat to enter through that input point.
Turning to FIG. 3, the air inlet tube 50 connects to the filter 55 by way of a connection point 60. This is a typical configuration for a system where the air filter is within a housing. Such an arrangement requires an interface between the air inlet tube and the housing.
The connection between the air inlet tube and the housing is also apparent in FIG. 4. In this figure the air inlet tube 65 extends through the housing 70. That intersection allows for heat transference. Heat enters the assembly even though the tube 65 is connected 75 to the filter 80.
Also apparent in each of the figures is that the bends in the tube creates turbulence, which can reduce the efficiency of the air flow to the engine.
What is needed is an interface air filter housing that filters ambient air, reduces heat dissipation between the air inlet tube and the housing, while being simple to install and maintain.